Generally a non-contact probe comprises of one or more emitter sources and one or more receivers. An emitter source projects waves, for example light waves, on the object of interest; the receiver(s) comprising for example a camera, capture(s) the returning waves from the object. For instance, if the receiver is a CCD-camera, it will take one or more shots of the object. By moving the object relative to the non-contact probe or vice versa, shots of the complete object can be taken, i.e. the object is being scanned. Each shot represents a one-dimensional (1D), two-dimensional (2D) or three-dimensional (3D) projection of the object depending on the physical form and working principle of the receiver(s). To obtain accurate 3D points on the surface of the object, relative to a fixed coordinate system, from multiple shots the following system parameters are preferably required:                1. the 3D position of the emitter source(s) relative to the receiver(s);        2. the 3D position and orientation of the emitted waves, relative to the receiver(s), coming from the emitter source(s);        3. the characteristics such as focal point of lenses of the receivers used in the non-contact probe;        4. the dimensions and measuring resolution of the receiver(s); and        5. the 3D position and orientation of the non-contact probe or the object relative to a fixed coordinate system, for each receiver capture.        
The actual values of the parameters 1 to 4 are calculated during the calibration. Some of the actual values of parameter 5 are calculated during the qualification procedure, others are given values readily obtainable from the object-non-contact probe, set-up. When these parameters are calculated for the given non-contact probe, the conversion, also called compensation, from receiver readings to accurate 3D points can be performed.
To be able to move the non-contact probe relative to the object, the probe is mounted on a localizer. This localizer can be a structure, portable or non-portable, on which the probe is mounted, like for example a tripod. This localizer can also be structure with moving axes, motorized or non-motorized, where the probe is mounted on the end of said axes, dependent to all other axes, like for example a robot, a milling machine or coordinate measuring machine (CMM). These last types of localizer can have the possibility to record the position and/or the rotation of the probe.
Some of the state-of-the-art techniques actually calculate parameters 1 to 5 explicitly using dedicated measurements in a sequential manner. Adjusting these parameters is difficult because of their complex interactions and adjustment can be time consuming.
Other state-of-the-art techniques for calibration and qualification do not calculate these parameters explicitly. In the first step, the receiver readings are first transformed in one, two or three dimensions, depending on whether the receiver itself is capable of measuring one, two or three dimensions. In this calibration step a receiver reading in receiver units is transformed to a point in e.g. SI units. The calibration can take several phenomena into account; for example, correcting the perspective since the object is not always parallel to the receiver or scaling correctly the readings. Finally, it must model correctly systematic reading errors in the receiver(s)—which is a complex operation.
The second step, the qualification, consists of determining the accurate position and orientation of the non-contact probe relative to a fixed coordinate system. The qualification procedure is generally performed by the end-user using special artifacts or other measuring equipment. The qualification procedure often requires an essential manual alignment of the artifact/measuring equipment with the non-contact probe.
Both steps, calibration and qualification, are based on some parameters that are tuned or optimized to obtain the 3D points accurately. All state of the art algorithms determine the values of the parameters for the two steps separately, usually scanning different artifacts with known features, dimensions, etc.
Although, it is easier to obtain few parameters at a time, this technique suffers from major drawbacks.
The various parameters have complex interactions and it is extremely difficult, if not impossible, to predict the effect of an individual parameter. Hence, an error at the very start can propagate and produce faulty results in the determination of the subsequent parameters. Unfortunately, there is as yet no correct method to back-propagate the information. As a result, even with the utmost care, the parameter fitting will be sub-optimal in the sense that the accuracy of the three-dimensional points will not be the best.
Another drawback of the de-coupled procedure is that it requires many high-level user interactions, which is time consuming and unreliable.
As a consequence, these techniques for calibration and qualification cannot be performed at the user's site, nor by the user itself.
To overcome these problems, the present invention provides a novel integrated approach using one single artifact. The present invention provides a novel method that computes all probe parameters in one single step using only one artifact. In this approach, a general function converts directly a receiver reading into a three dimensional point. This function corresponds to a sequence of calibration and qualification and therefore, depends on many parameters similar to the ones used in the classical de-coupled technique.
However, by expressing the conversion with one function, all interactions between the parameters are considered. Also, if the object being measured is known, the influence of a single parameter can directly be measured in terms of accuracy of the resulting 3D point.
The present invention provides a method to scan a known reference object and to use this information to find the values of the parameters that give the most accurate points. A single requirement of this method is the knowledge of the class of the reference object, like sphere or cube, box the actual sizes, aspect ratio, etc and a volume scan of the object. With these data, the entire procedure, calibration, and qualification is performed automatically.